The role of molecular conformation in the biological functions of some specifically acting, potent peptides is being sought. Nuclear magnetic resonance spectroscopy in the form of high resolution 1H and 13C spectra, and laboratory and rotating frame spin-lattice relaxation are the chief tools being used. The peptides under current study include the "opiate" pentapeptides and analogs, a chemotactic tripeptide, angiotensin and analogs.